1. Field of the Invention
The present invention generally relates to implantable medical devices. More specifically, the present invention relates to leads for implantable medical devices.
2. Description of the Related Art
Various implantable medical devices (IMD) utilize leads to deliver electrical stimulation to tissue, receive sensed electrical impulses from tissue, or transfer other sensor data indicative of a physical parameter. For example, implantable cardiac pacemakers, cardioverters, or defibrillators commonly have one or more leads connecting the device to cardiac tissue. The leads are often passed through a vein and guided into an atrial or ventricular chamber of the heart. Once so located, the distal end of the lead is properly positioned and often is secured.
Various techniques are employed to secure the distal end of the lead within the heart. For example, some lead tips include tines that engage fibrous tissue along the interior wall of the cardiac chamber. Over time, additional fibrous growth occurs that further secures the lead in position. Other leads include active fixation such as, for example, a helical tip that can be rotated into the cardiac tissue. Such a helical tip can serve as a fixation means, but may also serve as an electrode that is electrically coupled with one or more electrical conductors passing through the lead body. In use, the distal end of the lead is positioned in the selected location. The proximal end of the lead, or a portion thereof, is rotated which causes the helical tip to rotate and advance into the tissue. In order to facilitate this rotation, a clamping tool or wrench is coupled with the distal portion of the lead. Typically, the tool engages a connector pin and provides a larger gripping surface for the implanting physician to rotate. One such device is structured to engage the connector pin and provide an elongated pair of handles (scissor configuration) that extend perpendicular to a central axis of the connector pin. The implanting physician then grips a portion of the lead body distal to the connector pin and the rotates the tool in a plane perpendicular to the central axis until the helical tip is secured. Generally, such a wrench is relatively large and encumbers a large portion of the surgical field. Thus, wrench is typically only attached just prior to active fixation of the lead and is then removed. Furthermore, the “wrapping” action required to use the wrench may be cumbersome.
In addition, many leads are provided with a lumen disposed through the entirety of the lead body. The lumen may receive a guidewire that has been previously positioned, thereby allowing the lead to be directed to the proper location by passing over the guidewire. In such a case, the proximal end of the guidewire is inserted into the distal end of the lumen in the lead. Conversely, a stylet may be inserted into the lumen to provide a degree of rigidity to promote steerability of the lead in order to facilitate its passage into the proper position.
When a stylet is used, the distal end of the stylet is inserted into the proximal opening of the lumen in the lead and then advanced. To facilitate this insertion, a funnel is temporarily coupled with the connector. The funnel provides an enlarged opening and a guide through which the distal end of the stylet is inserted. The funnel guides the stylet into the narrower opening of the lumen in the connector pin. Once the stylet is inserted, the funnel generally remains in place. Thus, there is balance between providing a large opening to facilitate insertion while providing a small enough structure so as to minimize hindrance during the lead manipulation as well as fixation of the tip.